1. Field of the Invention
The present invention relates to an image-shooting apparatus capable of performing super-resolution processing to obtain a high-resolution image based on a low-resolution image obtained by shooting.
2. Description of Related Art
In recent years, there have been proposed various image-shooting apparatuses capable of so-called super-resolution processing, whereby a high-resolution image is obtained by use of a low-resolution image obtained by shooting. One example of such super-resolution processing is a method whereby one high-resolution image is generated by use of a plurality of low-resolution images.
In such a method whereby a high-resolution image is generated by use of a plurality of low-resolution images, the challenge is to reduce degradation in the individual low-resolution images. In particular, extreme degradation in low-resolution images is problematic because it prevents super-resolution processing from achieving its effect of increasing resolution. Specifically, if folding noise (aliasing—noise occurring in an image generated by capturing an optical image having a high spatial frequency equal to or higher than one-half (the Nyquist frequency) of the reciprocal 1/t of the pixel pitch t of an image sensor) is unlikely to occur in low-resolution images, it will be difficult to obtain the effect of enhancing resolution through cancellation of folding noise.
Cases where noise is unlikely to occur in low-resolution images include, for example, those where camera shake, subject motion, or the like occurring during shooting degrades images. In such cases, blurring of an image makes high-frequency components extremely small, and this makes folding noise unlikely to occur. Situations where camera shake, subject motion, or the like is likely to occur during shooting include, for example, those where the light entering an image-shooting apparatus is weak. In such cases, the shutter speed needs to be slow (the exposure time needs to be long), and this makes camera shake, subject motion, or the like likely.
Increasing the shutter speed may reduce camera shake, subject motion, or the like. Doing so, however, requires that the sensitivity of an image sensor be increased, and this causes a low-resolution image to contain noise. As a result, when a high-resolution image is generated, the noise in a low-resolution image is amplified, and this makes it difficult to obtain a satisfactory high-resolution image.